The present invention relates to high frequency power supplies for exciting gas-filled luminous tubes, for example, decorative and promotional neon signage. More specifically, the present invention pertains to alternative neon tube ballasting and hook-up topology that facilitates use of lower tension (voltage) power supply sources and, further, modular sign configurations that permit removal and/or substitution of sign segments.
Conventional neon signs consist of one or more series-connected neon or other gaseous tube segments. The "series" topology has been universally adopted to assure, in the first instance, substantially uniform current flow and corresponding brightness of each luminous tube segment. Further, the series configuration has heretofore been mandated by the ionization potential and negative resistance characteristics of the gaseous luminous tube, itself, which characteristics result in a substantial reduction in tube operating voltage once gas excitation has occurred. This latter property, in turn, virtually guarantees that one or more tubes--if connected in parallel--will not excite or illuminate with equal intensity.
The series configuration, however, is not without its limitations. One such limitation, for example, pertains to the maximum system operating voltage. Successively higher tension (voltage) power supplies--as required to operate correspondingly larger neon signs--create a host of insulation, arcing and corona problems. Thus, the practical upper voltage limit in the neon sign industry is considered to be about 15 KV. And, indeed, even this voltage may be unrealistically high in special situations where, for example, movable neon segments (e.g. clock hands) may require slip-connections capable of operating at full system voltage.
It is well known that luminous tube excitation and sustaining (operating) voltages are proportional to tube lengths. Thus, the 15 KV limit translates to a maximum sign length between 30 and 100 feet. And it is important to remember that this maximum is true without regard to whether the sign is comprised of a single neon tube or the series connection of plural tube segments--the overall length of all segments cannot exceed the 100 foot limit. Where larger (longer) signs are desired, prior designs have required the use of multiple power supplies.
A second restriction--common to all series-configured elements--is the fact that an interruption of current flow through any element causes the cessation of current through all elements. Thus, the removal of any tube segment in a conventional neon sign results in the corresponding shut-down of sign tube elements.
One object of the present invention is the ability to achieve a modular neon sign system in which one or more modules may be removed or substituted without disabling normal illumination of the remaining sign tube segments or modules. This feature advantageously permits use of a common sign that may be field fitted, or retrofitted, with site-specific removable sign modules.
A further and inherent disadvantage of conventional series topology relates to Kirchoff's current law, namely, the same magnitude current must pass through sign elements. In many situations this "limitation" may, in fact, be deemed a positive attribute as it assures substantially equal illumination of sign segments. In the present context, however, in particular where differing and removable sign modules are contemplated, the equal-current limitation is seen to unduly restrict artistic options.
It is well known that neon signs require some form of series impedance or ballast when powering neon tubes from a voltage source. This impedance is almost universally found as "leakage inductance" in the power supply transformer--and this is true whether the supply is of the standard line frequency step-up transformer variety or the increasingly popular high frequency oscillator/invertor configuration.
Use of capacitive ballasting has not worked well in the past, particularly in connection with standard 60 Hz supplies, due to the inability of this technique to control instantaneous tube currents. More specifically, upon gas avalanche a massive current spike is induced which may result in tube flickering and eventual electrode damage. Capacitive ballasting, however, has been found to work so long as the operating frequency of the power supply is maintained above the neon tube time constant (i.e. 1/2.pi.f.sub.o &lt;T) . Frequencies above 15 KHz meet this requirement for both neon and mercury, the two most common gases utilized in so-called "neon" signage.
As a consequence of the above, one embodiment of the present invention contemplates use of a relatively low voltage constant voltage power source, for example 3 KV, coupled to plural, parallel-configured neon elements or modules--each module comprised of a neon tube segment and an associated capacitor which capacitor is preferably integrated into the module interconnection system. The actual supply voltage is selected to assure proper excitation of the longest tube contemplated. Whatever the voltage, it will be appreciated that a substantially lower voltage will be required as compared to the alternative sign in which the same tube elements are employed, but arranged in the conventional series configuration.
Several important features, in addition to reduced supply tension, are achieved with the above-described individually ballasted neontube elements. First, any neon element may be removed with little or no effect on the continued ordinary operation of remaining neon elements. Thus, greater sign flexibility is obtained whereby sign elements or "modules" may be added, substituted, or removed as required to achieve a desired site-specific message.
A further advantage of this multiple ballasting topology is the ease by which individual neon tube currents (and corresponding illumination intensities) may be controlled to facilitate artistic flexibility. As tube current is directly proportional to ballast capacitance, individual tube intensities may be selected or changed by corresponding capacitor selections. No longer must tubes operate at the same intensity.
As noted, a feature of the present invention is the modular construction whereby a neon tube segment may be removed or substituted without otherwise interrupting proper sign operation. To this end, it is contemplated that modules may be electrically, if not mechanically, interconnected through employment of a pair of electrode receptacles. In a preferred arrangement, each receptacle would comprise and define a cylindrical recess into which an electrode end of a neon tube would be received. It is further contemplated that a metallic spring would be positioned in each receptacle to receive and electrically interconnect to the electrode.
Ballasting capacitors may be fabricated from appropriate ceramic material advantageously formed as discs of diameter corresponding to that of the receptacle whereby the capacitor may be positioned between the receptacle spring and neon tube electrode end. It will be appreciated that the precise ceramic material, the thickness and metallic plating area thereon are each parameters that, in accordance with known principles, may be appropriately selected to achieve the desired capacitance and ballasting effect. It is contemplated that these capacitance "buttons" may be inserted, as separate and independent components, into the receptacles or they may affixed by appropriate means to the electrode ends of the neon tube segments thereby defining integral modules for insertion into the receptacles. In either event, it is contemplated that the capacitance buttons sh be easily removable to facilitate the interchange of capacitance values as may be desired.
In another embodiment of the present invention, a sign is comprised of plural parallel neon elements including a fixed portion and one or more detachable modules. Unlike the above-described sign in which plural capacitance-ballasted modules are connected in parallel across a constant voltage power supply, the fixed portion of this second embodiment is not ballasted and is connected across a more-conventional constant current supply, albeit one of reduced tension. The fixed portion may be a single neon segment or it may be multiple series-connected tube sections. It will be appreciated, however, that the over length of the fixed section, and therefore the corresponding voltage of the power supply, will be significantly lower than that of conventional sign topology by reason of the effective transfer or relocation of the neon comprising the modules from an otherwise series string to a parallel connection.
The neon modules in this second embodiment are substantially as discussed above. Each is preferably received within a pair of receptacles and each incorporates appropriate current limiting, ceramic ballasting capacitor. Ballasting capacitors are not required in connection with the fixed portion of the sign by reason of the inherent current limiting afforded by the constant current supply, across which the fixed portion is connected.
It will be appreciated that the constant current supply and the fixed portion of the neon sign cooperate to generate the constant voltage output required by the capacitance-ballasted modular portions of the sign. More specifically, the voltage across the fixed neon portion of the sign is substantially constant once the neon gas has been excited into conduction. The fixed portion is, in essence, performing the dual function of, first, a sign element and, second, a voltage regulator.
It is therefore an object of the present invention to facilitate a modular sign topology whereby one or more modules may be removed, substituted, or added to the sign without adversely impacting the normal operation thereof.
It is a further object of the present invention that the sign modules may be installed or removed without great effort preferably admitting of field service in connection with same.
It is another object of the present invention that the illumination intensities of the various neon segments, in particular the modular portions, may differ and may be independently selected.
It is yet another object of the present invention that the power supply operate at lower voltages than those of conventional sign topologies for a given over length of neon tube.
These and various other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the embodiments and the drawings wherein:
FIG. 1 is a block representation of the reduced tension modular neon sign system of the present invention;
FIG. 2 is a block representation of another embodiment of the reduced tension modular neon sign system of the present invention;
FIG. 3 is an elevation view, partially in section, of the modular neon tube receptacle of the present invention;
FIG. 4 is an elevation view, partially in section, of the receptacle of FIG. 3 shown with the electrode tube end of a neon segment inserted therein; and,
FIG. 5 is a elevation view, partially in section, of the receptacle of FIG. 4 shown with the ceramic ballasting capacitor therein.